MirBSD manpage: perlintern(1)

PERLINTERN(1)   Perl Programmers Reference Guide    PERLINTERN(1)


     perlintern - autogenerated documentation of purely internal
                Perl functions


     This file is the autogenerated documentation of functions in
     the Perl interpreter that are documented using Perl's inter-
     nal documentation format but are not marked as part of the
     Perl API. In other words, they are not for use in exten-

CV reference counts and CvOUTSIDE

             Each CV has a pointer, "CvOUTSIDE()", to its lexi-
             cally enclosing CV (if any). Because pointers to
             anonymous sub prototypes are stored in "&" pad
             slots, it is a possible to get a circular reference,
             with the parent pointing to the child and
             vice-versa. To avoid the ensuing memory leak, we do
             not increment the reference count of the CV pointed
             to by "CvOUTSIDE" in the one specific instance that
             the parent has a "&" pad slot pointing back to us.
             In this case, we set the "CvWEAKOUTSIDE" flag in the
             child. This allows us to determine under what cir-
             cumstances we should decrement the refcount of the
             parent when freeing the child.

             There is a further complication with non-closure
             anonymous subs (i.e. those that do not refer to any
             lexicals outside that sub). In this case, the
             anonymous prototype is shared rather than being
             cloned. This has the consequence that the parent may
             be freed while there are still active children, eg

                 BEGIN { $a = sub { eval '$x' } }

             In this case, the BEGIN is freed immediately after
             execution since there are no active references to
             it: the anon sub prototype has "CvWEAKOUTSIDE" set
             since it's not a closure, and $a points to the same
             CV, so it doesn't contribute to BEGIN's refcount
             either.  When $a is executed, the "eval '$x'" causes
             the chain of "CvOUTSIDE"s to be followed, and the
             freed BEGIN is accessed.

             To avoid this, whenever a CV and its associated pad
             is freed, any "&" entries in the pad are explicitly
             removed from the pad, and if the refcount of the
             pointed-to anon sub is still positive, then that
             child's "CvOUTSIDE" is set to point to its
             grandparent. This will only occur in the single
             specific case of a non-closure anon prototype having

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             one or more active references (such as $a above).

             One other thing to consider is that a CV may be
             merely undefined rather than freed, eg "undef &foo".
             In this case, its refcount may not have reached
             zero, but we still delete its pad and its "CvROOT"
             etc. Since various children may still have their
             "CvOUTSIDE" pointing at this undefined CV, we keep
             its own "CvOUTSIDE" for the time being, so that the
             chain of lexical scopes is unbroken. For example,
             the following should print 123:

                 my $x = 123;
                 sub tmp { sub { eval '$x' } }
                 my $a = tmp();
                 undef &tmp;
                 print  $a->();

                     bool    CvWEAKOUTSIDE(CV *cv)

Functions in file pad.h
             Save the current pad in the given context block

                     void    CX_CURPAD_SAVE(struct context)

             Access the SV at offset po in the saved current pad
             in the given context block structure (can be used as
             an lvalue).

                     SV *    CX_CURPAD_SV(struct context, PADOFFSET po)

             Get the value from slot "po" in the base (DEPTH=1)
             pad of a padlist

                     SV *    PAD_BASE_SV(PADLIST padlist, PADOFFSET po)

             |CLONE_PARAMS* param Clone the state variables asso-
             ciated with running and compiling pads.

                     void    PAD_CLONE_VARS(PerlInterpreter *proto_perl \)

             Return the flags for the current compiling pad name
             at offset "po". Assumes a valid slot entry.

                     U32     PAD_COMPNAME_FLAGS(PADOFFSET po)

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             The generation number of the name at offset "po" in
             the current compiling pad (lvalue). Note that
             "SvCUR" is hijacked for this purpose.

                     STRLEN  PAD_COMPNAME_GEN(PADOFFSET po)

             Sets the generation number of the name at offset
             "po" in the current ling pad (lvalue) to "gen".
             Note that "SvCUR_set" is hijacked for this purpose.

                     STRLEN  PAD_COMPNAME_GEN_set(PADOFFSET po, int gen)

             Return the stash associated with an "our" variable.
             Assumes the slot entry is a valid "our" lexical.

                     HV *    PAD_COMPNAME_OURSTASH(PADOFFSET po)

             Return the name of the current compiling pad name at
             offset "po". Assumes a valid slot entry.

                     char *  PAD_COMPNAME_PV(PADOFFSET po)

             Return the type (stash) of the current compiling pad
             name at offset "po". Must be a valid name. Returns
             null if not typed.

                     HV *    PAD_COMPNAME_TYPE(PADOFFSET po)

     PAD_DUP Clone a padlist.

                     void    PAD_DUP(PADLIST dstpad, PADLIST srcpad, CLONE_PARAMS* param)

             Restore the old pad saved into the local variable
             opad by PAD_SAVE_LOCAL()

                     void    PAD_RESTORE_LOCAL(PAD *opad)

             Save the current pad to the local variable opad,
             then make the current pad equal to npad

                     void    PAD_SAVE_LOCAL(PAD *opad, PAD *npad)

             Save the current pad then set it to null.

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                     void    PAD_SAVE_SETNULLPAD()

             Set the slot at offset "po" in the current pad to

                     SV *    PAD_SETSV(PADOFFSET po, SV* sv)

             Set the current pad to be pad "n" in the padlist,
             saving the previous current pad. NB currently this
             macro expands to a string too long for some com-
             pilers, so it's best to replace it with


                     void    PAD_SET_CUR(PADLIST padlist, I32 n)

             like PAD_SET_CUR, but without the save

                     void    PAD_SET_CUR_NOSAVE(PADLIST padlist, I32 n)

     PAD_SV  Get the value at offset "po" in the current pad

                     void    PAD_SV(PADOFFSET po)

     PAD_SVl Lightweight and lvalue version of "PAD_SV". Get or
             set the value at offset "po" in the current pad.
             Unlike "PAD_SV", does not print diagnostics with
             -DX. For internal use only.

                     SV *    PAD_SVl(PADOFFSET po)

             Clear the pointed to pad value on scope exit. (i.e.
             the runtime action of 'my')

                     void    SAVECLEARSV(SV **svp)

             save PL_comppad and PL_curpad

                     void    SAVECOMPPAD()

             Save a pad slot (used to restore after an iteration)

             XXX DAPM it would make more sense to make the arg a
             PADOFFSET      void SAVEPADSV(PADOFFSET po)

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Functions in file pp_ctl.c
             Locate the CV corresponding to the currently execut-
             ing sub or eval. If db_seqp is non_null, skip CVs
             that are in the DB package and populate *db_seqp
             with the cop sequence number at the point that the
             DB:: code was entered. (allows debuggers to eval in
             the scope of the breakpoint rather than in the scope
             of the debugger itself).

                     CV*     find_runcv(U32 *db_seqp)

Global Variables

             When Perl is run in debugging mode, with the -d
             switch, this SV is a boolean which indicates whether
             subs are being single-stepped. Single-stepping is
             automatically turned on after every step.  This is
             the C variable which corresponds to Perl's
             $DB::single variable.  See "PL_DBsub".

                     SV *    PL_DBsingle

             When Perl is run in debugging mode, with the -d
             switch, this GV contains the SV which holds the name
             of the sub being debugged.  This is the C variable
             which corresponds to Perl's $DB::sub variable.  See

                     GV *    PL_DBsub

             Trace variable used when Perl is run in debugging
             mode, with the -d switch.  This is the C variable
             which corresponds to Perl's $DB::trace variable.
             See "PL_DBsingle".

                     SV *    PL_DBtrace

             The C variable which corresponds to Perl's $^W warn-
             ing variable.

                     bool    PL_dowarn

             The GV which was last used for a filehandle input
             operation. ("<FH>")

                     GV*     PL_last_in_gv

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             The output field separator - $, in Perl space.

                     SV*     PL_ofs_sv

     PL_rs   The input record separator - $/ in Perl space.

                     SV*     PL_rs

GV Functions

             Returns "TRUE" if given the name of a magical GV.

             Currently only useful internally when determining if
             a GV should be created even in rvalue contexts.

             "flags" is not used at present but available for
             future extension to allow selecting particular
             classes of magical variable.

             Currently assumes that "name" is NUL terminated (as
             well as len being valid). This assumption is met by
             all callers within the perl core, which all pass
             pointers returned by SvPV.

                     bool    is_gv_magical(char *name, STRLEN len, U32 flags)

IO Functions

             Function called by "do_readline" to spawn a glob (or
             do the glob inside perl on VMS). This code used to
             be inline, but now perl uses "File::Glob" this glob
             starter is only used by miniperl during the build
             process. Moving it away shrinks pp_hot.c; shrinking
             pp_hot.c helps speed perl up.

                     PerlIO* start_glob(SV* pattern, IO *io)

Pad Data Structures

             CV's can have CvPADLIST(cv) set to point to an AV.

             For these purposes "forms" are a kind-of CV, eval""s
             are too (except they're not callable at will and are
             always thrown away after the eval"" is done execut-

             XSUBs don't have CvPADLIST set - dXSTARG fetches
             values from PL_curpad, but that is really the call-
             ers pad (a slot of which is allocated by every

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             The CvPADLIST AV has does not have AvREAL set, so
             REFCNT of component items is managed "manual"
             (mostly in pad.c) rather than normal av.c rules. The
             items in the AV are not SVs as for a normal AV, but
             other AVs:

             0'th Entry of the CvPADLIST is an AV which
             represents the "names" or rather the "static type
             information" for lexicals.

             The CvDEPTH'th entry of CvPADLIST AV is an AV which
             is the stack frame at that depth of recursion into
             the CV. The 0'th slot of a frame AV is an AV which
             is @_. other entries are storage for variables and
             op targets.

             During compilation: "PL_comppad_name" is set to the
             names AV. "PL_comppad" is set to the frame AV for
             the frame CvDEPTH == 1. "PL_curpad" is set to the
             body of the frame AV (i.e. AvARRAY(PL_comppad)).

             During execution, "PL_comppad" and "PL_curpad" refer
             to the live frame of the currently executing sub.

             Iterating over the names AV iterates over all possi-
             ble pad items. Pad slots that are SVs_PADTMP
             (targets/GVs/constants) end up having &PL_sv_undef
             "names" (see pad_alloc()).

             Only my/our variable (SVs_PADMY/SVs_PADOUR) slots
             get valid names. The rest are op
             targets/GVs/constants which are statically allocated
             or resolved at compile time.  These don't have names
             by which they can be looked up from Perl code at run
             time through eval"" like my/our variables can be.
             Since they can't be looked up by "name" but only by
             their index allocated at compile time (which is usu-
             ally in PL_op->op_targ), wasting a name SV for them
             doesn't make sense.

             The SVs in the names AV have their PV being the name
             of the variable. NV+1..IV inclusive is a range of
             cop_seq numbers for which the name is valid.  For
             typed lexicals name SV is SVt_PVMG and SvSTASH
             points at the type.  For "our" lexicals, the type is
             SVt_PVGV, and GvSTASH points at the stash of the
             associated global (so that duplicate "our" declara-
             tions in the same package can be detected).  SvCUR
             is sometimes hijacked to store the generation number
             during compilation.

             If SvFAKE is set on the name SV then slot in the

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             frame AVs are a REFCNT'ed references to a lexical
             from "outside". In this case, the name SV does not
             have a cop_seq range, since it is in scope

             If the 'name' is '&' the corresponding entry in
             frame AV is a CV representing a possible closure.
             (SvFAKE and name of '&' is not a meaningful combina-
             tion currently but could become so if "my sub foo
             {}" is implemented.)

             The flag SVf_PADSTALE is cleared on lexicals each
             time the my() is executed, and set on scope exit.
             This allows the 'Variable $x is not available' warn-
             ing to be generated in evals, such as

                 { my $x = 1; sub f { eval '$x'} } f();

                     AV *    CvPADLIST(CV *cv)

             Clone a CV: make a new CV which points to the same
             code etc, but which has a newly-created pad built by
             copying the prototype pad and capturing any outer

                     CV*     cv_clone(CV* proto)

     cv_dump dump the contents of a CV

                     void    cv_dump(const CV *cv, const char *title)

             Dump the contents of a padlist

                     void    do_dump_pad(I32 level, PerlIO *file, PADLIST *padlist, int full)

             "Introduce" my variables to visible status.

                     U32     intro_my()

             Add an anon code entry to the current compiling pad

                     PADOFFSET       pad_add_anon(SV* sv, OPCODE op_type)

             Create a new name in the current pad at the speci-
             fied offset. If "typestash" is valid, the name is
             for a typed lexical; set the name's stash to that
             value. If "ourstash" is valid, it's an our lexical,

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             set the name's GvSTASH to that value

             Also, if the name is @.. or %.., create a new array
             or hash for that slot

             If fake, it means we're cloning an existing entry

                     PADOFFSET       pad_add_name(char *name, HV* typestash, HV* ourstash, bool clone)

             Allocate a new my or tmp pad entry. For a my, simply
             push a null SV onto the end of PL_comppad, but for a
             tmp, scan the pad from PL_padix upwards for a slot
             which has no name and no active value.

                     PADOFFSET       pad_alloc(I32 optype, U32 tmptype)

             Update the pad compilation state variables on entry
             to a new block

                     void    pad_block_start(int full)

             Check for duplicate declarations: report any of:
                  * a my in the current scope with the same name;
                  * an our (anywhere in the pad) with the same
             name and the same stash
                    as "ourstash" "is_our" indicates that the
             name to check is an 'our' declaration

                     void    pad_check_dup(char* name, bool is_our, HV* ourstash)

             Find a named lexical anywhere in a chain of nested
             pads. Add fake entries in the inner pads if it's
             found in an outer one. innercv is the CV *inside*
             the chain of outer CVs to be searched. If newoff is
             non-null, this is a run-time cloning: don't add fake
             entries, just find the lexical and add a ref to it
             at newoff in the current pad.

                     PADOFFSET       pad_findlex(const char* name, PADOFFSET newoff, const CV* innercv)

             Given a lexical name, try to find its offset, first
             in the current pad, or failing that, in the pads of
             any lexically enclosing subs (including the compli-
             cations introduced by eval). If the name is found in
             an outer pad, then a fake entry is added to the
             current pad. Returns the offset in the current pad,
             or NOT_IN_PAD on failure.

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                     PADOFFSET       pad_findmy(char* name)

             For any anon CVs in the pad, change CvOUTSIDE of
             that CV from old_cv to new_cv if necessary. Needed
             when a newly-compiled CV has to be moved to a pre-
             existing CV struct.

                     void    pad_fixup_inner_anons(PADLIST *padlist, CV *old_cv, CV *new_cv)

             Free the SV at offset po in the current pad.

                     void    pad_free(PADOFFSET po)

             Cleanup at end of scope during compilation: set the
             max seq number for lexicals in this scope and warn
             of any lexicals that never got introduced.

                     void    pad_leavemy()

     pad_new Create a new compiling padlist, saving and updating
             the various global vars at the same time as creating
             the pad itself. The following flags can be OR'ed

                 padnew_CLONE        this pad is for a cloned CV
                 padnew_SAVE         save old globals
                 padnew_SAVESUB      also save extra stuff for start of sub

                     PADLIST*        pad_new(int flags)

             Push a new pad frame onto the padlist, unless
             there's already a pad at this depth, in which case
             don't bother creating a new one. If has_args is
             true, give the new pad an @_ in slot zero.

                     void    pad_push(PADLIST *padlist, int depth, int has_args)

             Mark all the current temporaries for reuse

                     void    pad_reset()

             Set the entry at offset po in the current pad to sv.
             Use the macro PAD_SETSV() rather than calling this
             function directly.

                     void    pad_setsv(PADOFFSET po, SV* sv)

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             Abandon the tmp in the current pad at offset po and
             replace with a new one.

                     void    pad_swipe(PADOFFSET po, bool refadjust)

             Tidy up a pad after we've finished compiling it:
                 * remove most stuff from the pads of anonsub
                 * give it a @_;
                 * mark tmps as such.

                     void    pad_tidy(padtidy_type type)

             Free the padlist associated with a CV. If parts of
             it happen to be current, we null the relevant
             PL_*pad* global vars so that we don't have any dan-
             gling references left. We also repoint the CvOUTSIDE
             of any about-to-be-orphaned inner subs to the outer
             of this cv.

             (This function should really be called pad_free, but
             the name was already taken)

                     void    pad_undef(CV* cv)

Stack Manipulation Macros

     djSP    Declare Just "SP". This is actually identical to
             "dSP", and declares a local copy of perl's stack
             pointer, available via the "SP" macro. See "SP".
             (Available for backward source code compatibility
             with the old (Perl 5.005) thread model.)


     LVRET   True if this op will be the return value of an
             lvalue subroutine

SV Manipulation Functions

             Print appropriate "Use of uninitialized variable"

                     void    report_uninit()

             Given a chunk of memory, link it to the head of the
             list of arenas, and split it into a list of free

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                     void    sv_add_arena(char* ptr, U32 size, U32 flags)

             Decrement the refcnt of each remaining SV, possibly
             triggering a cleanup. This function may have to be
             called multiple times to free SVs which are in com-
             plex self-referential hierarchies.

                     I32     sv_clean_all()

             Attempt to destroy all objects not yet freed

                     void    sv_clean_objs()

             Deallocate the memory used by all arenas. Note that
             all the individual SV heads and bodies within the
             arenas must already have been freed.

                     void    sv_free_arenas()


     The autodocumentation system was originally added to the
     Perl core by Benjamin Stuhl. Documentation is by whoever was
     kind enough to document their functions.


     perlguts(1), perlapi(1)

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